diff --git a/core/includes/bootstrap.inc b/core/includes/bootstrap.inc
index b442aae..e7108e7 100644
--- a/core/includes/bootstrap.inc
+++ b/core/includes/bootstrap.inc
@@ -1297,7 +1297,7 @@ function drupal_serve_page_from_cache(stdClass $cache, Response $response) {
   // response to reply to a subsequent request for a given URL without
   // revalidation.
   if (!isset($boot_headers['vary']) && !settings()->get('omit_vary_cookie')) {
-    $response->setVary('cookie', FALSE);
+    $response->setVary('Cookie', FALSE);
   }
 
   if ($page_compression) {
diff --git a/core/modules/system/lib/Drupal/system/Tests/Bootstrap/PageCacheTest.php b/core/modules/system/lib/Drupal/system/Tests/Bootstrap/PageCacheTest.php
index 5bab747..62244e5 100644
--- a/core/modules/system/lib/Drupal/system/Tests/Bootstrap/PageCacheTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/Bootstrap/PageCacheTest.php
@@ -98,7 +98,7 @@ function testPageCache() {
     // Fill the cache.
     $this->drupalGet('system-test/set-header', array('query' => array('name' => 'Foo', 'value' => 'bar')));
     $this->assertEqual($this->drupalGetHeader('X-Drupal-Cache'), 'MISS', 'Page was not cached.');
-    $this->assertEqual($this->drupalGetHeader('Vary'), 'cookie,accept-encoding', 'Vary header was sent.');
+    $this->assertEqual($this->drupalGetHeader('Vary'), 'Cookie,Accept-Encoding', 'Vary header was sent.');
     // Symfony's Response logic determines a specific order for the subvalues
     // of the Cache-Control header, even if they are explicitly passed in to
     // the response header bag in a different order.
@@ -109,7 +109,7 @@ function testPageCache() {
     // Check cache.
     $this->drupalGet('system-test/set-header', array('query' => array('name' => 'Foo', 'value' => 'bar')));
     $this->assertEqual($this->drupalGetHeader('X-Drupal-Cache'), 'HIT', 'Page was cached.');
-    $this->assertEqual($this->drupalGetHeader('Vary'), 'cookie,accept-encoding', 'Vary: Cookie header was sent.');
+    $this->assertEqual($this->drupalGetHeader('Vary'), 'Cookie,Accept-Encoding', 'Vary: Cookie header was sent.');
     $this->assertEqual($this->drupalGetHeader('Cache-Control'), 'max-age=300, public', 'Cache-Control header was sent.');
     $this->assertEqual($this->drupalGetHeader('Expires'), 'Sun, 19 Nov 1978 05:00:00 GMT', 'Expires header was sent.');
     $this->assertEqual($this->drupalGetHeader('Foo'), 'bar', 'Custom header was sent.');
@@ -118,7 +118,7 @@ function testPageCache() {
     $this->drupalGet('system-test/set-header', array('query' => array('name' => 'Expires', 'value' => 'Fri, 19 Nov 2008 05:00:00 GMT')));
     $this->assertEqual($this->drupalGetHeader('Expires'), 'Fri, 19 Nov 2008 05:00:00 GMT', 'Default header was replaced.');
     $this->drupalGet('system-test/set-header', array('query' => array('name' => 'Vary', 'value' => 'User-Agent')));
-    $this->assertEqual($this->drupalGetHeader('Vary'), 'User-Agent,accept-encoding', 'Default header was replaced.');
+    $this->assertEqual($this->drupalGetHeader('Vary'), 'User-Agent,Accept-Encoding', 'Default header was replaced.');
 
     // Check that authenticated users bypass the cache.
     $user = $this->drupalCreateUser();